Download Managing Infectious Diseases on Dairies

Managing Infectious Diseases on Dairies
Franklyn Garry
Professor, Integrated Livestock Management
Colorado State University
It is every dairy producer’s concern to maintain strong markets for dairy products of all kinds,
including milk and dairy animals that leave the farm. The profitability of dairy operations is
closely linked to the health of the market channels used to sell their products. In turn, the
health of those markets is linked to numerous factors that contribute to consumer confidence
and demand. To maintain consumer confidence requires that dairy producers can assure that
their animals are healthy and well cared for, and that the animals and their products do not
represent any health risk to the public at large. Therefore, efforts that maintain a healthy herd
reward the producer by increasing productivity, and also by minimizing consumer risk and
assuring consumer confidence. There are numerous on-farm management practices that can
help accomplish these goals.
The Spectrum of Cattle Health Problems
Over the last several decades, changes in management, nutrition and genetics of our cattle
population have led to a shift in the type of diseases perceived to be important. We
increasingly recognize the importance of suboptimal performance that occurs without overt
disease signs, the occurrence of metabolic and production related diseases and a variety of
management problems that limit performance but are not directly related to specifically
diagnosed diseases. Examples of these types of problems include rumen acidosis, ketosis and
fatty liver disease, laminitis, hypocalcemia/milk fever, displaced abomasums, and reproductive
inefficiency.
Enough emphasis has been placed on this variety of problems that it is easy to perceive that
infectious disease is proportionally less of a problem now than it was in times gone by. Recent
information from the National Animal Health Monitoring System Dairy '96 Study
demonstrates, however, that infectious diseases still represent a tremendous area of concern.
This study estimates that clinical mastitis occurs in 13.4% of all dairy cows, respiratory
problems in 2.5%, lameness in 10.5%, and diarrhea in 3.4%. In dairy calves, scours, diarrhea
and respiratory problems are responsible for 85% of all calf deaths.
Infectious disease problems represent a special concern for other reasons besides their high
frequency of occurrence. Some of these diseases can spread from animal to animal (that is,
they are contagious), and some of them can spread to other animals, including humans. These
diseases are costly due to the animal losses they produce, as well as the treatment and
prevention costs they incur.
Not only are infectious diseases costly to the producer, but they also represent concerns to the
consumer of dairy products. This is the group of diseases for which antibiotics are used, thus
posing risks of chemical residues. Injection sites from various treatments and preventives
decrease the meat quality from market cows. Most importantly, some infectious agents can
contaminate products for human consumption and represent a special food safety threat.
Clearly, the spectrum of cattle health issues is very broad, both in terms of the types of disease
problems, and the management required to deal with these problems. These issues range from
non-infectious to infectious diseases, from nutritional management to vaccination strategies,
from antibiotic residue concerns to food safety issues. It is evident to anyone involved in cattle
production that health problems are central to many of the management decisions that need to
be made on a daily basis.
Dairy Infectious Diseases
Ongoing scientific advancements influence our perception of disease and our methods of
dealing with these problems. With advances in computer technology and animal monitoring
techniques, we have increased our ability to evaluate indices of herd performance and
productivity. Thus we look at reproductive performance, milk production, sick pen days, milk
somatic cell count, etc. to evaluate the herd. For some, increased knowledge about the impacts
of nutrition and animal management as primary determinants of livestock health has led them
to ignore many infectious disease issues. It has been easy to assume that vaccine improvements
make infections ever more preventable, and antibiotic improvements make these diseases ever
more treatable. Dairy producers and veterinarians have relied heavily on antibiotic treatment
and vaccination as the mainstays of their approach to infectious disease management. These
management steps are only a small subset of the procedures that can be employed. Good
biosecurity and hygeine practices have traditionally been underemployed, but represent an
equal or more important set of practices that can minimize the occurrence of these problems.
Dairy cattle are susceptible to many different infectious problems, ranging from those diseases
that virtually every dairy producer faces such as mastitis and calf scours, to those problems that
are currently not found in US dairies such as Foot and Mouth disease or Rinderpest. Those
problems found routinely and almost continually on an operation are called ‘endemic’, and
primarily challenge producers due to the ongoing losses they incur. Other problems, ranging
from dairy cow pneumonia to the foreign animal problems are uncommon or not present, but
are often typified by explosive, or ‘epidemic’ herd outbreaks when they occur. Many diseases
can occur at a low level on an operation for a period of time and then develop into more
widespread problems with higher occurrence rates. Therefore, producers should be concerned
about threats both from ongoing disease losses and from explosive new problems. While many
cattle diseases occur exclusively in cattle, and thus are ‘species specific’, other problems, like
salmonellosis or E. coli infection can readily occur in humans and other species.
Losses from ongoing infectious problems tend to be insidious. These losses can be attributed to
treatment costs, reduced productivity of affected animals, and animal death or culling losses. In
many cases the productivity losses are not prominent enough that they are easily seen by the
producer unless they are closely monitored. A good example of such a disease problem is
contagious mastitis, represented by Strep. ag infection. This is an extremely costly problem
even when mastitits is not clinically apparent because it reduces milk production and decreases
milk quality. Hairy heel warts, Johne’s disease, calf scours, calf respiratory disease, and
numerous other diseases are common on many farms, affect substantial numbers of animals,
and primarily cost producers by insidiously decreasing animal performance.
Diseases like salmonellosis may be present on a dairy, but only cause occasional cases of illness
for a prolonged time. Then, for reasons that may not be immediately apparent, the disease
incidence dramatically increases. Some diseases may not exist on a dairy, but are then introduced,
for example when purchased replacement animals arrive on farm. These problems are often seen
as outbreaks that affect large numbers of animals in a short time, such as Mycoplasma mastitis,
anaplasmosis, respiratory syncitial virus pneumonia.
Sooner or later, almost every producer faces a real crisis in animal health. This might occur as
a sudden increase in an infectious disease, a rapidly fatal disease of unknown cause, or
recognition that a certain problem has been increasing over a prolonged time and is now
rampant in the herd. When this occurs, several truisms become apparent:
1. Even with the best possible management, disease is a fact of life.
2. We can manage animals as a herd, but disease ultimately manifests in individual animals.
3. In a complex system, something goes wrong eventually.
While there are many ways we could respond to these observations, I believe the best approach
is the one least frequently employed. Keeping in mind the many different disease challenges
we need to consider, plus the many different factors that can promote disease, plus the many
different methods we might use to manage disease problems, there is no set of management
practices that could fit all situations. Clearly there is need to fit management to each individual
operation. This requires a balance between generic best management practices and monitoring
for the circumstances and disease problems of the dairy. Specifically this requires attention to
prompt and thorough diagnosis on a routine and systematic basis.
Infectious Disease Management
When an animal is infected by a disease-causing agent, that microorganism, or germ, can be
found in many tissues and body secretions. Animals or humans who consume these tissues,
contact the secretions, or contact the environment contaminated by body secretions will also be
exposed to that disease agent. If they are also susceptible to the infection, then they too can
become ill from contacting those contaminated materials. This is how infections can spread in a
population of cattle, and also how they can spread to humans.
Although some people have held the hope that we are defeating infectious disease problems with
the development of improved antibiotics and improved vaccines, the survey information above
shows that infectious disease problems are as great a concern as ever. In modern dairy operations
they have become even more important as dairies have increased size and animal density,
allowing rapid and effective transfer of the disease agents between animals.
The public health concerns that arise from infectious dairy problems can be directly affected by
dairy management. Every dairy needs a disease monitoring and management program. These
programs need to consider which diseases are present, which ones can be minimized or
prevented, how infections are identified and treated, what safeguards are in place to minimize
disease spread and to minimize the likelihood of public health problems, etc.
What methods can a dairy producer use to manage infectious disease in dairy cattle, and to
minimize human health risks? Appropriate vaccination is a very useful method of minimizing
disease occurrence or severity. Treatment protocols can be tailored to optimize animal cure rates
and to minimize likelihood of human exposure to antibiotics. Most importantly, biosecurity
procedures and good hygeine can minimize the occurrence and spread of infectious disease
agents. It is extremely important to recognize what each of these control methods can and cannot
do and to use all of them appropriately in an overall disease control program.
Vaccination is the most commonly used method of preventing infectious disease in livestock
populations. Unfortunately, many people have become eager to believe that vaccination is our
most powerful weapon in disease prevention, to the point where they rely almost exclusively on
vaccines as the primary disease prevention method. In reality, vaccination is only one of several
disease control methods, it is useful only when used in combination with other control methods,
and it is not as powerful as some of the other tools available.
Even with the tremendous advances in vaccine technology that we have seen over the last several
decades, very few vaccines are capable of preventing infection or disease development. Vaccines
should be viewed more as modifiers of disease than as preventive agents. Vaccines can help an
otherwise healthy and well nourished animal diminish the effects of a disease agent, but can
rarely prevent the agent from infecting and multiplying in the body. This is an extremely
important point. Even for those disease agents where a vaccine has been developed, that vaccine
cannot eliminate the disease, and it’s important to note that vaccines are available for some, but
not all, of the important dairy cattle diseases.
Vaccines work by exposing the animal to an infectious disease agent before the animal is
naturally exposed to the infection. When the animal’s immune system recognizes that disease
agent it can mount a quicker and more effective response to infection when it is later exposed.
The vaccine increases the animal’s resistance to infection, and modifies the occurrence of disease
when infection does occur. If exposure to the disease agent is very high, as can occur with BVD
or environmental mastitis agents, then the animal will still get infected, but hopefully will not
become severely affected by disease. A true prevention program needs to incorporate methods
that decrease exposure to the disease-causing agent, and then vaccination is only one component
of the program. Vaccination can be very useful, but must be seen as a disease modifier, not as a
stand-alone preventive practice.
An extremely important concept to apply when developing a dairy disease prevention program, is
that the risk of infectious disease occurrence is a balance between animal resistance to infection
and the rate of that animal’s exposure to the disease agent. Vaccines help to increase animal
resistance, but do nothing to decrease exposure. With very few exceptions, even our most
advanced vaccines cannot make an animal absolutely immune to disease. Furthermore, disease
resistance depends on many factors beyond previous exposure to disease agents. All dairy
producers will recognize, for example, that fresh cows and baby calves have reduced disease
resistance even when good vaccine programs are in use. The risk of infectious disease
development in dairy animals is therefore very closely linked to the amount of exposure to
disease agents. It is extremely important that other methods beyond vaccination are employed to
decrease disease occurrence by decreasing exposure.
Antibiotics have been very extensively used for infectious disease control in livestock. Since
antibiotics were first discovered many years ago they have proven to be phenomenally useful for
combating bacterial infections and producers and veterinarians have come to rely on these
products as a mainstay in disease treatment. Countless dollars have been invested in the discovery
of new antibiotics and both humans and animals have benefited from these advances. Along the
way we have come to see that these chemicals can be both beneficial and harmful. Thus
infectious animal disease represents a potential human safety threat not just because of potential
transfer of disease causing agents, but also because of potential transfer of the chemicals we use
to combat the animal disease.
To be effective, antibiotics need to be applied at the right dose, at the right time, for the right
duration of treatment. Furthermore, each antibiotic has a different spectrum of activity, so we
need to use the right drug for a certain infectious disease. All of these conditions influence
whether the drug is capable of curing a disease, and we have come to realize that each antibiotic
has a limit to its’ efficacy. There is no ‘silver bullet’ drug, and appropriate use requires careful
decision making in the choice of treatment. Because these drugs are costly, there are many
circumstances where the costs of use are higher than the benefits of use. Again, careful decision
making is required to use an antibiotic appropriately.
Very importantly, these chemicals remain in the body for periods of time after their application.
While antibiotics may benefit the diseased animal, their presence in animal food products is now
recognized as a profound threat to consumers. Sufficient time must be allowed, before meat and
milk from a treated animal can be considered free of the chemical, and thus appropriate for
human consumption. Many bacteria have developed resistance to antibiotics. This has very
important implications both for animals and humans infected by these bacteria. For these resistant
bacteria, particular antibiotics are no longer useful in helping cure the disease. For all of these
reasons, antibiotics are not a ‘cure-all’ and must be used judiciously. It is extremely important to
have good disease identification processes, and good protocols for appropriate treatment.. Used
inappropriately, antibiotics can be ineffective, costly, present human health risks, and encourage
further bacterial resistance problems.
There are numerous infectious diseases of concern that do not respond well to vaccination and
treatment. Antibiotics are only effective in combating bacterial infections, and have no efficacy
against viral diseases. Because bacteria are very complex disease agents, we have very few
vaccines that are truly effective in combating bacterial disease. Many diseases exist as chronic
conditions that do not respond well to any currently available treatment. Some diseases are
characterized by the existence of ‘carrier’ animals that remain infected over prolonged periods
of time, shed the disease agents into the environment and infect additional animals, but unable
to clear the infection from its own body. Examples of diseases that exemplify these problems
include brucellosis, tuberculosis, Johne's disease, salmonellosis, bovine leukosis, mastitis due
to Streptococcus, Staphylococcus and Mycoplasma, anaplasmosis, hairy heel warts, ringworm,
Pasteurella pneumonia, Haemophilus, BVD, IBR, PI3 and BRSV.
There are many infectious diseases where vaccines and antibiotics are simply not useful.
Considering the preceding comments about the realities of vaccine and antibiotic use, there is a
pressing need for producers and veterinarians to rethink their approach to infectious disease
prevention and treatment. We cannot afford to look at infectious disease control as something we
can get ‘out of a bottle’.
Biosecurity Management
For the reasons discussed above, infectious disease management is very important to dairy
producers, and requires thoughtful investment in planning control procedures that limit spread of
infectious agents. These management procedures are needed to complement efforts to make
animals more resistant to infection. As stated earlier, infectious disease is influenced both by the
degree of resistance of an animal to infection, and also by the amount of exposure, or disease
pressure the animal faces. We can employ many management practices that reduce animal
exposure to infectious agents. A general term for such management efforts is biosecurity. When a
particular disease is not present on an operation, the ideal means to prevent the disease is to keep
the infectious agent off the farm. For widespread, endemic diseases that are present on most
farms, we can employ practices that minimize its spread to unaffected animals. Most of the
procedures that are useful for controlling infectious disease on a dairy are common sense,
hygienic, good management practices. Improving our approach to infectious disease control
requires a thoughtful review of dairy animal management with an eye towards decreasing
contamination of animals and their environment with materials that carry the infectious agents.
A look at the findings from the NAHMS Dairy '96 Study puts in perspective the opportunities
for improvement in this disease control area. Depending on herd size, between 45%-80% of
dairies brought cattle onto their operation within the year preceding the study. Of the new
additions, fewer than 25% were quarantined and even fewer were adequately tested for
infectious diseases. These statistics alone emphasize the high risk of infectious disease
introduction in most dairies. Between 20%-50% of dairies fail to require common
vaccinations before introducing new cattle into their herd. Thirty to eighty percent of dairies
fail to require milk somatic cell counts and 60%-90% of dairies request no milk culture before
introducing new herd replacements.
Unlike vaccines or antibiotics, which need to be specifically designed to fight specific disease
agents, most biosecurity management practices are useful in combating multiple problems at the
same time. The reason is that infectious agents share common pathways of spreading to new
animals. Therefore, management that decreases exposure to one infection, also decreases
exposure to other diseases at the same time. For example, many agents spread through manure
contamination, so decreasing exposure of calves to manure decreases exposure to all of those
agents. Similarly, keeping sick animals separate from susceptible herdmates, improving hygiene
of feeding equipment, using new or disinfected medical treatment equipment, assuring worker
hygiene, decreasing traffic between different groups of animals, separating calves from dams at
birth, pasteurizing milk for calves or using milk replacer, are all management practices that can
decrease spread of infectious agents.
Biosecurity management practices are also valuable in decreasing the likelihood that animal
diseases represent a threat to humans. By decreasing disease prevalence and spread of disease
agents we minimize the risks that those agents can spread to humans, and also decrease the
problems associated with our treatment methods, such as chemical residues in food products.
There is no magic formula for incorporating biosecurity practices into herd management. The
steps required to improve dairy herd health and reduce the occurrence and spread of infectious
diseases are logical and straightforward. It is important that the dairy producer and the herd
veterinarian work together closely to overview current herd status and implement changes. To
develop a sound management program, the producer should review and understand the important
diseases on the operation. These may be problems that have been previously identified, or that
represent serious risks that the producer wishes to avoid. In order to combat these problems, it is
important to have a basic understanding of how these problems affect the animals and how they
can spread on the dairy. It is also important to have an assessment of the current status of the
dairy with regard to these disease problems. In some cases the goal will be to prevent entry of a
disease, in other cases the disease is already present and the goal will be to reduce the occurrence
of the problem. For many operations, this second step will require a strategy for detecting and
measuring disease occurrence. With this information and focus, protocols for vaccination and
disease treatment can be scrutinized and updated. Management practices that decrease exposure
to infectious agents will then enhance the benefits of other herd health procedures, such as
nutritional management and vaccination.
A biosecurity program must be individually tailored to the herd and its specific concerns and
goals. Quarantine can help to limit the introduction of infectious agents that induce acute
disease, but quarantine alone is an insufficient measure for the prevention of entry of most of
the important infectious diseases. Other biosecurity measures will vary with the mode of
disease transmission, the duration of infectious agent shedding, the presence of asymptomatic
carriers, and the reliability of screening tests for the disease. Quarantine will not work to
prevent the introduction of diseases with chronic asymptomatic carrier states such as Johne's
disease, BVD, IBR, salmonellosis, BLV and contagious mastitis.
For some diseases, the best method of protection is testing prior to purchase. Screening tests
can be very useful for avoiding brucellosis, tuberculosis, contagious mastitis, BVD and BLV.
For Johne's disease, individual animal screening tests are inadequate and knowledge of the
Johne's disease status of the herd of origin is probably more important.
Screening tests for Salmonella can be useful but most Salmonella infections are caused by
feed, environmental contamination or spread by other species. Risk of disease transmission
from other species has been generally considered low but should not be forgotten when
considering herd management strategies. Tuberculosis and brucellosis can be spread by deer or
other cervids; sarcosporidiosis, hydatid disease and rabies can be spread from dogs; and
toxoplasmosis and rabies are commonly spread by cats. The Dairy '96 Study shows that 90%
of operations have contact between cattle and cats, 78% of operations have contact with dogs,
approximately 50% have contact with deer or other cervids, and 20% or less have contact with
beef cattle, horses or poultry. The study also demonstrated that 60% or fewer of dairies
prevented access to grain or concentrate storage units by dogs, cats, birds and rodents.
Infectious problems can be spread by contact with infected body fluids. More than 50% of
operations that dehorned heifers with spoons, gouges, saws or other surgical methods neither
washed nor disinfected between animals; 65%-75% of operations did not change needles or
disinfect needles between animals when administering vaccines by injection. Approximately
75% of operations used the same rectal sleeve for more than one cow when performing rectal
palpation. Only 18% of operations separated sick cows to prevent nose to nose contact with
other cows and heifers.
Some infectious diseases are spread from dams to newborns and the time of separation of the
calf from the cow can have an impact on the transmission of these diseases. Only 13% of
operations separated newborn calves from the dams within one hour of birth. Twenty-five
percent of operations separated the calves beyond 12 hours after birth. Fifteen percent of
operations allowed calves to stay with their dams more than 24 hours. Thirty percent of
operations failed to wash teats and udders before colostrum was collected for administration to
the calves. Approximately 55% of operations used the calving area as a hospital area for sick
cows. Fecal contamination is a common means for spread of many enteric infections.
Approximately 33% of operations used equipment for manure handling that was also used to
handle feed for heifers less than 12 months of age.
A well designed biosecurity program can have a very significant impact in reducing the risk of
infectious spread. The program should be designed for the needs of each individual operation.
Consideration should be given to entry of new animals, quarantine of new animals,
prepurchase vaccination and testing or screening for disease, knowledge of the herd of origin
for new purchases, minimization of feed and environmental contamination, disinfection of
instruments, minimized contact between sick and healthy cattle or dams and calves, minimized
fecal contamination, fly and other insect control programs, and minimized contact with other
species.
Monitoring Disease – The Importance of Accurate Diagnosis
So how do we determine the diseases of importance on an operation? While there are certain
management practices that generically help reduce the risk of spread of multiple disease
problems, others are very focused on specific diseases. Virtually all of the management items
discussed above require that good diagnostic tools are used, or at least that the diagnostic tools
used are well understood and employed properly, even when they are not particularly accurate.
Additionally, there are unexpected disease problems that occur even when management against
disease is well implemented. Unfortunately, it is often the unexpected problems that can cause
the greatest losses, exactly because they are unanticipated and therefore unmanaged until they
are well advanced.
The most important tool for adapting management to a changing set of disease concerns is
prompt and accurate diagnosis. The best opportunities for disease monitoring are typically
overlooked. It seems that many producers and veterinarians assume that they have a good feel
for the diseases that occur on a specific operation. Alternatively, they assume they can use a
good guess on the nature of a disease and manage around the problem. Perhaps they feel that
the set of likely problems is limited enough that they don’t really need to know the cause of a
specific disease. Or perhaps it seems reasonable to apply some ‘shotgun’ treatment and
prevention practices with the assumption that a broad enough approach is likely to be
successful regardless of the specific problem at hand.
There is a saying that “You can’t manage what you don’t measure”. While this is not
completely true, it is certainly true that the more closely you can identify and measure a
problem, the better equipped you are to manage it.
For whatever reason, very few producers or veterinarians take advantage of the array of
diagnostic techniques available. When diagnostic methods are employed, they are often used
sparingly in bits and pieces, and rarely with a well thought out approach. In other words, it is
common that we deal with dairy disease issues without thorough information about the nature
and extent of disease problems. Often an operation will have good information about overall
herd production parameters, but fail to get routine disease information about individual sick
animals. Some of this information is easily acquired and often quite reasonably priced,
especially when compared with the value of the information for making herd decisions.
A dead animal is usually viewed as a waste product, one that brings the burden of disposal.
The value of the dead animal is routinely overlooked. It is true that dead animals are a loss to
the operation, but they also provide an invaluable opportunity to evaluate an aspect of the herd.
Post mortem examination (necropsy examination) is one of the most underutilized tools in herd
monitoring and management. It is important to investigate death losses systematically and to
record trends observed over time.
The signs of many cattle diseases are remarkably similar and physical examination of sick
animals can often fail to provide an accurate diagnosis. For many treatment scenarios this is
not a major problem, because some diseases respond to similar treatments, and because
treatment regimens can be modified to improve recovery, in many cases without a final
definitive diagnosis. On the other hand, the most effective and cost beneficial strategies both
for prevention and treatment will be devised on the basis of accurate diagnosis and disease
identification. Therefore, routine examination of dead animals on an operation provides one of
the best opportunities to evaluate treatment and prevention.
Necropsy examination on a routine and systematic basis, preferably on every dead animal,
provides a tremendous advantage in the face of an emerging disease outbreak. Many of the
procedures performed on samples submitted to a diagnostic laboratory require time. Waiting to
conduct necropsies and submit samples until it has become really clear that a major disease
problem is underway is a very poor plan. Typically by the time you are obliged to submit
necropsy samples, substantial losses have already occurred, and more will continue to occur
before a reasonable answer is available. These losses are compounded by the waste of poorly
directed treatment measures and other costly interventions.
A typical example follows to emphasize these points. A lactating dairy cow dies within 24
hours of getting sick with apparent respiratory disease. Because of the sudden onset and rapid
death, and because only one cow was affected, the operator shrugs it off. Several years ago
respiratory syncitial virus infection had occurred in some animals in the herd. Consulting with
the veterinarian, the owner becomes convinced this cow was likely an aberrant case of
infection with that agent. Two days later another cow dies, followed by several more cows
over the succeeding week and a half. Several different treatments are tried, but none with good
success, leading the owner and veterinarian to believe more strongly in the original diagnosis,
because they don’t expect antibiotics to affect the outcome of this viral disease. Unfortunately
the disease problem appears to be escalating, and when six cows are dead, and several others
surviving but left as respiratory cripples, three new cases appear on the same day. One of these
dies, and the other two are euthanized. Necropsy of all three reveals severe bacterial
pneumonia, and culture and sensitivity of the organism reveals the best antibiotic to use.
However, three more cows are lost while these results are pending. After changing the
treatment approach to treat at the first signs of respiratory illness with the right drugs, no
further losses occur, and all affected cows respond well to the treatment.
Not all disease problems are as quickly resolved as this case. The point of this illustration was
to stimulate the following questions. How many sick animals and how much money would
have been saved if the first dead cow had been subjected to necropsy? How many cows do you
have to lose before you initiate a good diagnostic workup? How long do you wait before
realizing that a problem may be different from what you first expected? How much more
money would have been lost if the owner above had instituted a radical change in vaccination
programs with an assumed diagnosis that was wrong?
The best diagnostic necropsy is one performed on a recently dead animal. Sometimes it is
important to euthanize an animal for necropsy because the diagnostic value exceeds the
likelihood that the animal will respond favorably to treatment. In such cases, it is important to
carefully select an animal that has the same disease signs, is recently affected by the disease,
and thus closely fits the disease scenario you are trying to combat.
Summary
Cattle health problems are very important concerns for producers, playing a central role in
many aspects of daily management. Cattle diseases have many different causes and
manifestations. Depending on the circumstances of each operation the problems that face
producers will have some similarities, but usually differ greatly from farm to farm. The best
approach to managing ongoing disease problems, and heading off new disease threats before
they become major problems, is a combination of 1.) management practices targeted to control
the diseases of importance on the operation, plus 2.) ongoing diagnosis and monitoring of
disease problems, necessary for modifying the management program. Necropsy and diagnostic
sample submission are key elements of a disease monitoring program.